This invention relates to an apparatus and method combining optical and electronic devices, which can include laser apparatus, for position sensing and inspection of a target such as a workpiece.
The invention herein described was made in the course of or under a contract, or a subcontract thereunder, with the Unites States Department of the Air Force.
A wide variety of methods and apparatus for performing a function which can generally be referred to as range or position finding have been reported in various forms of the literature. An important application for such apparatus, and one in which the present invention is particularly useful, involves the location and inspection of a workpiece in connection with which it is desired to control a metal removal tool. Such tools can include laser apparatus, for example, to drill, melt, cut or otherwise operate on a workpiece, as well as a variety of mechanical metal removal tools such as grinders, cutters, drills, etc. Other forms of such range finding apparatus have been applied to non-material removal apparatus such as the automatic focusing photographic slide projectors.
One type of apparatus, the operational performance of which is improved through the use of the present invention, is shown in Duston et al -- U.S. Pat. No. 3,806,829. That reference contains a detailed description of a four-axis numerically controlled workpiece support as well as other automatic or programmed features and functions which constitute a typical complete laser drilling or welding system. However, no provision is made for automatic focus finding or hole inspection methods.
Taniguchi et al -- U.S. Pat. No. 3,689,159 disclose a laser apparatus for automatically shaping a workpiece. A monitor light, separate from the shaping laser, is directed toward and reflected from the workpiece along the same axis as is the shaping laser, the relfected light being directed to a light detector through a vibrating plate for positioning control. However, the response and accuracy of such a system is not adequate for such applications as the accurate drilling of small air cooling holes in an aircraft engine component such as turbine blades and nozzles.
Other apparatus, such as that shown in Conner et al -- U.S. Pat. No. 3,449,542, employ mirrors or similar devices for reflecting a specular image from a workpiece rather than scattered reflected light from a workpiece in order to provide position control. In the Conner et al apparatus, laser drilling point variations are controlled by deflecting the laser beam on the workpiece. Other devices such as that of Chiou et al -- U.S. Pat. No. 3,485,996 depend on a difference in reflected light brightness or intensity reflected from the workpiece back along the incident beam for sensing different materials and triggering laser operation.
The disclosures of each of the above-mentioned patents are incorporated herein by reference.